In 2030, elderly people will represent 20% of the US population. The focus of our work is on the mechanism(s) causing fibrosis and diastolic dysfunction, which has become epidemic in the aging population. Our overall objective is to examine cellular and molecular interactions between fibroblasts of two developmental origins (mesenchymal and myeloid) and potential rescue approaches to reduce diastolic dysfunction and cardiac fibrosis in the aging heart. The central hypothesis arose from our data in which we identified the signaling abnormalities in mesenchymal fibroblasts that directly contribute to their aberrant activation resulting in fibrosis and stimulation of monocyte influx into the heart. Infiltrating monocytes polarize into myeloid fibroblasts and further contribute to mesenchymal fibroblast pathological activation. To examine the contribution of each fibroblast type and their interaction, we will use specific inhibitors such as 1) AICAR, an AMPK activator that inhibits the pathologically upregulated Erk pathway in mesenchymal fibroblasts and thereby reduces collagen and fibronectin levels in the aging heart and 2) DCSL-1, which specifically binds to DC-SIGN, a receptor found exclusively in leukocytes. We have found that in vivo DCSL-1 treatment improves cardiac function and decreases the number of M1 proinflammatory macrophages and myeloid fibroblasts in the heart as well as reducing collagen deposition. In SA1, we will determine the mechanism by which defective mesenchymal fibroblasts contribute to interstitial fibrosis in the aging heart and examine the role of an AMPK activator in reversing these defects. We will examine the molecular mechanism by which pathological matrix deposition occurs in aged mouse and human tissues using electron microscopy, mass spectrometry and signaling pathway activation analyses. We will also determine the impact of in vivo and in vitro AICAR on these processes. Finally, the changes in cardiac fibrosis and function after in vivo AICAR treatment in mice will be monitored by noninvasive MRI, Echo and Doppler measurements. In SA2, we will investigate the role of the inflammatory infiltrate in fibrosis and in the altered mesenchymal fibroblast phenotype by use of a myeloid- specific inhibitor, DCSL1. We will compare aged mice treated with DCSL-1 with age-matching controls and study infiltrating leukocytes via noninvasive cell tracking using MRI, analyze infiltrating monocytes and lymphocytes via mass cytometry and identify cytokines secreted by them via protein array. Furthermore, the role of DCSL-1 on T lymphocyte populations will be investigated using adoptive transfer. For in vitro studies the effect of secreted cytokines on mesenchymal fibroblasts of mouse and human origin will be analyzed as well. Finally, matrix analysis and cardiac function study to compare DCSL-1 and control treated aged mice will be done as in SA1. This approach is innovative and significant because it will allow us to link changes in cardiac function to molecular and cellular responses. Furthermore, our Preliminary Data shows a correlation of the mouse model with the human aging heart, where we observed the same defects.